Transducer



May 3, 1966 E. v. CARLSON TRANSDUCER 2 Sheets-Sheet 1 Original Filed Sept. 6, 1961 E. V. CARLSON May 3, 1966 TRANSDUCER 2 Sheets-Sheet 2 Original Filed Sept. 6, 1961 INVENTOR. a%m%@m United States Patent 3,249,702 TRANSDUCER Elmer V. Carlson, Prospect Heights, Ill., assignor to Industrial Research Products, Inc., Franklin Park, 11]., a corporation of Delaware Original application Sept. 6, 1961, Ser. No. 136,220.

Divided and this application Sept. 1, 1964, Ser. No. 393,619 7 13 Claims. (Cl. 179-115) .This invention relates to improvements in miniature electromechanical transducers of the type wherein a portion of an armature is vibratable in the air gap of a magnetic circuit. This application is a division of applicants copending application Serial No. 136,220, which was filed September 6, 1961,-for a Transducer.

In these vibratable armature-type transducers, thearmature is positioned inside a coil of Wire arranged to link a magnetic flux that flows along the armature in one direction or the other. One portion of the armature is in an air or working gap between two flux conductive surfaces having opposed polarities established by one or more magnets. When the portion of the armature in the working gap is at zero potential, there is no flow of flux along the armature. When this zero potential of that portion of the armature in the working gap ceases, as by flux induced by the coil in a receiver or by a diaphragm or stylus moving the armature toward one of the faces of the working gap in a microphone, flux flows along the armature. Flux flowing along the armature in either direction is frequently called the fluctuating or alternating flux to contrast with the steady unidirectionalflux at the working gap, although the two are in fact components of the total flux of the system.

One Way of maintaining that portion of the armature in the working gap at zero potential is to position two magnets on opposite sides of the working gap, to connect the opposite poles of the two magnets to each other by a flux conductor, and to fix one end of the armature at or near the midpoint of this flux conductor.

An object of this invention .is to adapt the idea of utilizing a magnetic case as both a shield and a part of the magnetic circuit of the transducer motor presented in copending application, Serial No. 27,006, now United States Letters Patent No. 3,111,563, dated November 19, 1963, to a transducer having the flux circuit described in the preceding paragraph.

Another object of this invention is to provide an improved path for the fluctuating or alternating flux that flows along the armature at points outside the armature. This fluctuating flux must complete its circuit'through the shells and probably through the magnets themselves. This weak flux encounters much resistance in moving through either one of the central pole pieces so that the sensitivity of the device would be low. A feature of this invention is the provision of pole pieces at the faces of the gaps, each pole piece in contact with a permanent magnet, and additionally of an extension on each pole piece which is turned toward the flux-conductive case so as to enable the weak, alternating magnetic flux to be shunted around the magnets.

Another object of this invention is to adjust the position of the vibratable portion of an armature in the, .working gap firstly, without touching the armature; secondlygwithout bending it; thirdly, after the diaphragm is in position, and fourthly, while the case is sealed. Applicant pivots one end of the armature at the internal wall of the case with means externally of .the case for moving the armature on the pivot. A feature of the present invention is the mounting of one end of an armature between two externally projecting tongues at "ice a joint in the case, but making the juncture of the case with the tongues of a bendable material so that by bending the tongues with respect to the case, the free end of the armature positioned in a working gap within the case may be moved toward one pole or the other of the gap. The armature is not touched. The centering can be done not only after the diaphragm is mounted, but after the case is sealed. 7 Another object of this invention is to establish a rigid relationship between the bendable flanges of the thin walled case to the working gap. One of the features of this invention is a magnet stack which in combination with straight flanges and side walls hold the parts in rigid relationship during the setting of the armature. The case being made of somewhat ductible material so that the flanges may be bent, must be reinforced so that bending of the flanges has no effect on the position of the magnet stack'with respect to the held end of the armature. This magnet stack is provided with structural members at right angles to the plane of the work ing gap so that the case of the transducer may be clamped at the opposite ends of the magnet stack, and when so held, the flanges may be worked with precision.

Another object of this invention is to provide a transducer whose dimension along a line at right angles to the plane of the armature is minimal. Heretofore, the diaphragm has been spaced laterally of the armature so that the dimension of the case must be increased to provide some vibration space between the diaphragm and the motor and space for the front cavity. Two features of this invention are the mounting of a diaphragm in a space longitudinally adjacent the working end of the armature and positioning the plane of the diaphragm substantially in the plane of the armature.

Another object of this invention is to more rapidly, accurately relate the components of the transducer to each other during assembly. A feature of this invention is the building of the operating components of the transducer as separate entities whose external walls will exactly seat against the inside walls of a complementarily designed case. The front cavity is a complete cavity in itself. The magnet stack is a complete assembly with the pole faces accurately spaced. 1 The coil and leads are a rectangular parallelepiped, and the case is formed of a ductile material of U-shaped configuration so that the various components may be slipped in and the whole clamped together.

These and such other objects as may hereinafter appear are attained in the embodiment of the invention disclosed in the accompanying drawings, wherein:

FIGURE 1 is a longitudinal, vertical section taken along the line 1-1 of applicants transducer set forth in FIG- URE 2;

FIGURE 2 is a section along the line 2- 2 of FIG- URE 1;

FIGURE 3 is a section taken along the line 33 of FIGURE 1;

FIGURE 4 is an end view of the assembled transducer;

FIGURE 5 is an exploded view of the component parts of the transducer when ready for assembly;

FIGURE 6 is a perspective view of the pole piece having a projecting tab or ear;

FIGURE 7 is a View in a section of a combined armacurediaphragm with Thuras tube incorporated therein in proportionate relationship with the corresponding parts in FIGURE 1; and,

FIGURE 8 is a plan view of the diaphragm shown in FIGURE 7.

Continuing to refer to the drawings, applicants transducer consists of a case 16 which is made of flux-conductive material selected for its ability to carry both an intense It is not bent.

3 steady flux and a superimposed fluctuating or alternating flux. The case is somewhat pear shaped, see FIGURE 5, and consists of a diaphragm and magnet or main chamber 25 and a coil chamber 27. The main chamber 25 has end wall 18, top wall 26 and bottom wall 32. It is joined to the coil chamber 27 by shoulders 28 and 30 leading to top wall 38 and bottom wall 40. The end 29 of the case 16 has two flanges 34 and 36 between which is positioned one end of an armature 48, which together form an adjustable tongue. The flanges and armature .are joined by welding or brazing. The sides of the case, 94 and 96,

A coil 42 is disposed around the armature 48 and may be held in position either by encapsulating the coil in a form which seats exactly between the walls 38, 40, 94 and 96, or by mounting the coil on the armature. Under this construction, the coil tunnel clears the surface of the armature 48 by a distance sufficient to permit free movement of the armature within selected limits. In some applications, the coil may be mounted on the armature in which case clearance is provided between the outer walls of the coil and the inside walls of the case.

Mounted on that end of the main chamber which is adjacent to the coil 42 is a magnet pole piece stack 49 consisting of bar magnets 56 and 58. To improve the path for the alternating or fluctuating flux, applicant provides pole pieces 52 and 54, spaced by lugs 61 and 63 mounted on members 68 and 62 respectively, said members 60 and 62 being of material of low flux conductivity.

The bar magnets are elongated with respect to the axis of magnetization, but their shape depends upon the particular configuration of the case. The magnets are disposed so that their maximum potential difference is disposed across the gap 64 between the pole pieces 52 and 54. The pole pieces 52 and 54 have extensions 80 and 82 respectively which extend toward the adjacent top 26 and bottom 32 of the case.

The main cavity 25 is occupied principally by a diaphragm 68 and front sound chamber 72. This sound chamber cavity 72 is a complete receptacle in itself consistingof a tub 70 having outer dimensions adapted to seat firmly in the lower portion of the cavity 25. The

open side of the tub 70 is closed by a vibratable diaphragm 69 to the surface of which is affixed a substantially rigid plate 66. Two openings in the sound chamber are shown, but only one will be used for a given application. If an opening at the end is desired, a port 20 is formed in.the end wall 18 of the case 16 and a tube 24 may be inserted therein. To provide access to the outer sound chambers 72, an opening 76 is provided in the wall of the tub 70. If a lateral opening is desired, aligned ports 71 may be placed in the tub 70 and case bottom 32.

The armature 48 projects to the left of the magnet stack 49 by a distance suflicient to reach the diaphragm plate 66 and its end is attached thereto as for example, by a spot of adhesive 69. The end of the armature could be carried further to the left and centered over the rectangular plate 66. The plate 66 and the armature could be in a common plane joined by adhesive between the edge of the plate 66 and the end of the armature 48. Under certain conditions, the plate 66 and armature can be integral.

Mounting the diaphragm substantially in the plane of the armature eliminates the connecting member usually found in those transducers and the diaphragm provides limited support for the free end of the armature. When a transducer is dropped and the shock is along a vector at an angle to a flat surface of the armature, the momentum of an armature end mayplace a bend or set at, for example, the edge 83 of the upper edge of the pole piece 54..

Applicants construction shows an armature rigidly supported at one end and flexibly supported at theother end with an intermediate portion vibratable in a working gap.

' and magnet 58, along dot-dash line 87..

The transducer shown may be used as either a microphone or a receiver. Where used as a microphone, it may be equipped with a Thuras or inertance tube mounted on the diaphragm and formed in the plate 66. This .Thuras tube is similarto the type shown in Knowles Patent No. 2,966,558, and consists of two tubes 77 and 79, both formed as a groove in plate 66. Referring to FIG- URE 2, tube 79 opens into the top of the plate 66 at 91,

see also FIGURE 1, and through a hole'81' in the diaphragm into the front or outer sound chamber 72. The other tube 77 opens similarly on opposite sides of the diaphragm. The tubes are dynamically balanced on the diaphragm so that they do not interfere with vibration.

While the foregoing transducer could be fabricated in various ways, applicant has devised subassemblies which promote exact predetermined relationship between the partsl Referring to FIGURES, the top, bottom and ends are part of a single stamlping which includes mating grooves to form the parts and 92 for the terminal posts for the coil leads. The: coil 42 is encapsulated or enshrouded suificiently to define its external dimensions and its vertical thickness is such that when the coil is positioned between the walls 38 and 40: and'the armature is positioned in the tunnel 50 of the coil 42 with the arms of the T between the flanges 34 and 36, all in a jig, the flanges may be welded, soldered or brazed to the armature and the walls 38 and 40 will hold the armature with mechanical clearance to the walls of the tunnel 50.

The elements of the magnet stack 49 are preassembled with adhesive and the stack slipped in laterally of the shell 16 to the left of the end of the armature, see FIG- URE 1. It is then moved to the right, the working gap 64 being slipped over the armature 48, and under pres sure from the top .and bottom of the case, is cemented in the position shown in FIGURE 1. The tub with diaphragm mounted therein is pushed into the cavity 75 and the end of the armature 48 is: attached to the diaphragm plate 66 by a spot of adhesive 69. Separate sides 94 and 96 may be attached, or a side wall assembly 98 having a protective end wall 100 with aligned openings may beused.

The foregoing sequence of assembly may be varied. Thus the top wall may be spread back and the units 70, 49, 48, 4-2, positioned on the bottom 32 and then the top 36 brought around.

The unit 98 incorporates both side walls and end wall and has a protective shield 100 with through openings 101 and 103 which register withopenings 90 and 92.-

This may be slipped over the end of the open-sided case 16 and by suitable means such as resistance welding, the entire case may be sealed.

In FIGURES 7 and 8, there is shown a second embodiment of the invention wherein the armature and diaphragm are a single member and the Thuras tube is in that member. The armature isidentified by the numeral and its fixed end 122 is held between the flanges 34 and 36 as in the first embodiment. The, pole pieces 52 and 54 and magnets 56 and 58 occupy the same relative position as shown in FIGURE- 1. The second cross arm 1 24 of the T, however, constitutes the piston head of the diaphragm and hence replaces the plate 66 of FIGURE 1.

diaphragm.

Having thus described his invention, what applicant claims is:

1. An electro-acoustic transducer comprising an elongated case, a motor mounted in one end of the case, an armature extending lengthwise of the case and having a vibratable portion in said motor, and a diaphragm positioned in the other end of the case and forming a front sound cavity, said diaphragm being drivingly connected to the vibratable portion of the armature of the motor.

2. The electro-acoustic transducer of claim 1 wherein the external opening into the sound cavity is through that end of the case containing the diaphragm.

3. An electro-acoustic transducer comprising a case, a motor mounted in the case, said motor having a leaf-type armature, one end of the armature being fixed adjacent one wall of the case and the other being vibratable in a flux gap of the motor near the center of the case, and a diaphragm positioned adjacent the vibratable end of the armature away from the motor near the plane of the armature and sealed to the inside of the case to form a frontsound cavity, said diaphragm being mechanically connected to the vibratable portion of the armature.

4. An electro-acoustic transducer comprising an elongated case made of flux-conductive material having two opposite end walls, a leaf-type armature having one end mounted on one end wall of the case and the other end extending parallel to the major axis of the case, a magnet mounted on each side of the armature and spaced therefrom to form a working gap, each magnet being in fluxconductive contact with the case, a diaphragm enclosing a portion of the other end of the case to form a front sound cavity, an opening through the case into said cavity, and means drivingly connecting the vibratable portion of the armature to the diaphragm.

5. An electro-acoustic transducer comprising an elongated case having opposite end walls, a motor mounted in one end of the case, a drive element on said motor having a portion vibratable along a line normal to the length of the case, anda diaphragm positioned in the other end of the case and forming a front sound cavity, the plane of V vibratable diaphragm closing the open side of said receptacle, an opening through the wall of the case and the wall of the receptacle into the receptacle, a magnet stack mounted within the case adjacent said receptacle, said stack comprising two magnets separated by spacer members forming a workinggap with opposite poles of the magnets facing each other, and with the opposed poles of the two magnets in engagement with the flux-conductive walls of the case respectively, a coil mounted adjacent the magnet stack on the side away from the sound receptacle with the axis of the coil penetrating the Working gap, and a leaf-type armature mounted flux-conductively on the wall of the case and passing through the coil and the working gap to a point beyond, and means drivingly connecting the armature to the diaphragm.

8. The transducer of claim 7 wherein the magnet stack consists of two side members having median spacing lugs against the opposite sides of which the magnets may be pressed and wherein the opposite ends of the spacing members engage the opposite inside surfaces of the case.

9. The transducer of claim 7 wherein the outside dimensions of the coil in a plane parallel to the surface of the armature are engaged by the walls of the case and are held in fixed relationship to the armature and the magnet stack.

10. A transducer comprising a case formed of three components, all components being flux conductive; the first component comprising a single piece of sheet material bent to a U-shaped cross section wit-h the free ends closed to form outwardly projecting flanges, a leaf-type, fiux-conductive armature having one end sealed between said flanges and the other end extending inwardly of the case, a coil around the armature adjacent the flanges and positioned by the walls of the case, and a magnet stack comprising two magnets spaced by a working gap with the outer ends of the magnets flux-conductively connected to the case and positioned inwardly adjacent the coil, and a diaphragmsealing off a portion of the inside of the case adjacent the end of the armature to form a front sound cavity, said diaphragm being drivingly connected to the armature; and second and third components comprising side walls for said case.

11'. The transducer of claim 10 in which the second and third components are joined by a U-shaped member whose base portion is a channel that seats over the two flanges on the first component.

12. The electro-acoustic transducer of claim 1 wherein the diaphragm and the armature are integral.

1 3. The electro-acoustic transducer of claim 1 wherein the diaphragm and the armature are integral and lie in a common plane.

No references cited.

ROBERT H. ROSE, Primary Examiner.

F. N. CARTEN, Assistant Examiner. 

1. AN ELECTRO-ACOUSTIC TRANSDUCER COMPRISING AN ELONGATED CASE, A MOTOR MOUNTED IN ONE END OF THE CASE, AN ARMATURE EXTENDING LENGTHWISE OF THE CASE AND HAVING A VIBRATABLE PORTION IN SAID MOTOR, AND A DISPHRAGM POSITIONED IN THE OTHER END OF THE CASE AND FORMING A FRONT SOUND CAVITY, SAID DIAPHRAGM BEING DRIVINGLY CONNECTED TO THE VIBRATABLE PORTION OF THE ARMATURE OF THE MOTOR. 